Test and focusing means for light signals



Oct. 1941.

M. R. DOUGLASS TEST AND FOCUSING MEANS FDR LIGHT SIGNALS Filed Feb. 10,1940 -HZS ATITORNEY Patented Oct. 7, 1941 Myrl R. Douglass, Edgewood,Pa., assignor to The Union Switch 8; Signal Company, Swissvale, Pa., acorporation Pennsylvania Application February 10, 1940, Serial No.318,383

1 Claim.

Myinvention relates to testing and focusing means for :light signals.

In certain forms of light signals, such, for example, as that disclosedin Letters Patent f the United States, No. 2,230,853, grantedto WesleyB. Wells on February 4, 1941, for Light signals. a light projecting unitconsisting of a lamp having a concentrated filament located at the focalpoint-of an ellipticalreflector is intended to be replaceably secured inplace in the light signal by preadjusted means which insures that anysimilar unit will be accurately positioned relative to the other opticalelements of the signal. The lamp employed in each light projecting unitis of the precision type, thatis to say, of the type which has itsfilament positioned relative to the lamp base with sufficient accuracy50 that it can be interchanged with a similar, lamp without changing theoptical characteristics of the light projecting unit, and in orderthatthe units and lamps can both be interchangedin the intended mannerand still maintain the maximum signal efllciency, it is essential thatall reflectors and lamps should come up to a certain standard ofexcellence, and also that the sockets in which the lamps are mountedshould oe positioned relative to the reflector during manufacture with.suflicient accuracy so that any lamp which is in service in the socketwill have its filament located exactly at the focal point of thereflector.

One object of my present invention is to provide a device which willenable the lamps and reflectors of light projecting units of the typedescribed to be quickly and conveniently tested to ascertain that theycome up to the required degree of excellence, and which will also enablethe lamp socket of any light projecting unit to be quickly andaccurately located in the, position with respect to theassociatedreflector in which all precision lampswhich are placed in the socketwill have their filaments accurately located at the focal point of thereflector.

According to my invention, the device comprises a series of lenses andstop plates provided with peep holes all disposed in a frame betweendetachable mounting means for the light units and a light sensitive cellconnected to a suitable meter, in such manner that the axes of alllenses, peep holes, and the light sensitive element of the lightsensitive cell all coincide exactly with the axis of the reflectormounting means, whereby when a light unit is mounted on the mountingmeans with the lamp illuminated and the socket is adjusted to theposition in which the lamp filament is located at the focal point of thereflector, a maximum meter reading will be obtained.

Other objects and characteristic features of my invention will appear asthe description proceeds.

I shall describe one form of device embodying my invention, and shallthen features thereof in the claim.

In the accompanying drawing, Figs. 1, 2 and 3 are front elevational,right-hand and left-hand end views, respectively, showing one form ofdevice embodying my invention.

Similar reference characters refer to similar parts in all three views.

Referrin to the'drawing, the device in the form here shown comprisesthree parallel rods I, 2 and 3 disposed at the three corners of anisosceles triangle, and mounted at their .ends in spaced end plates 4and 5 secured to a suitable base 5. Formed in the end plate 4 is anopening l which aligns axially with an opening 8 formed in the end plate5, and provided on the outer side of the end plate-4 are suitable meanswhich I will describe presently for supporting a light unit in aposition to project the rays of light emerging from the unit through theopening 1 toward the opening 8 in an axial direction.

The light unit may assume a variety of forms, but inasmuch as the deviceembodying my invention is particularly suitable for, although in no. waylimited to, use with a light unit of the type shown and described in thepreviously re- Ierre'd to Wells Patent No. 2,230,853, I have chosen toillustrate my invention in connection with this type of light unit.

This unit,,which is designated as a whole by the point out the novelreference character A, comprises an elliptical re-' flector 20 mountedin a metal case 2|," and an electric lamp 22, the filament of which isintended to be located at one of theconjugate foci of the reflector 20.The rear wall oi the casing 2| is provided with three rearwardlyprojecting studs 23, arranged in triangular'formation, and mounted onthese studs betwecn compressed coil springs 24 which surround the shankportions of the studs and nuts 25 which are adjustably screwed onto theouter ends of the studs, is a plate 26. This plate carries a socket 21which projects with some clearance through a hole 28 formed in the rearwall of the casing 21, and serves as a support for the previouslyreferred to electric lamp 22. Mounted on the studs 23 outside of thenuts 25 are lock nuts 29 for securing the nuts 25 in adjusted positions.It will be apparent that by adjusting the nuts 25, the position of thelamp filament with respect to the reflector may be varied, thus enablingthe lamp filament to be accurately positioned'atthe focal point of thereflector, and hence permitting the maximum efficiency to be obtainedfrom the light unit.

The light unit further comprises three radial arms 38, 3| and 32 each ofwhich is formed with 'a socket 33. These sockets are adapted to receiveof the light issuing from the lamp 22 from strikingthelens l3.

As is well understood, the light emerging from the lens M will be in theform of a beam of parallel rays, and these rays are directed onto thelens l5. This lens is also of the clear glass planoconvex type, and isso arranged and so constructed that it will convert the parallel beamthe studs and will be yieldably held in a flxed position. The studs areso adjusted that when the light unit is'in place on the studs and thefilament of the lamp 22 is accurately located at the one focal point ofthe reflector, the other focal point will be located on the axial lineextending between the two openings 1 and 8. For the purpose of holdingthe studs in their adjusted position lock nuts 4! are provided on theinner ends of the studs.

It will be apparent that with mounting means of the type shown the lightunits may be quickly secured to and removed from the end plate 4,whereby testing of the units is greatly facilitated.

A light sensitive cell 9 is secured to the end plate 5 in back of theopening 8, and is connected by means of a wire Illa to a meter l0secured to the base plate 6 adjacent the light unit A. The lightsensitive cell is so arranged that the axis of its light sensitiveelementwill coincide with the axis of the opening 8, and that any lightwhich passes through the opening 8 will strike this element,--wherebythemeter lflwill indicate the intensity of the light energy passing throughthe opening 8.

Supported by the rods l, 2 and 3 between the two'end plates 4 and 5 is astop plate ll provided with an opening Ha, a stop plate I2 provided withan opening 12a, a lens l3 mounted in a plate i3a, a lens 14 mounted in aplate l4a, a lens I5 7 mounted in a plate I5a, and a vided with anopening lBa.

The two lenses l3 and I4 are of the well-known clear glassplano-convex'type, and together form a doublet which is identical withthat-employed in actual practice in light signals of the type in whichthe light projecting unit A is intended to be used. The axis of thedoublet coincides with the axis of the openings I and 8 in the endplates 4 and 5, and thedoublet is so positioned that when the light unitA is in place on the studs 35, 38 and 31, the focal point X of thedoublet will coincide exactly with the conjugate focus of the reflectorof the light unit.

The two stop plates II and '12 are disposed on opposite sides of thefocal point X, and the plate II is so located and has its opening Ha ofsuch size that the cone of light which is concentrated bythe reflectorat the point X will'just pass through the opening. The plate I! is solocated and has its opening l2a of such size that only a sufficientamount of light passing through the focal point X to exactly cover thelens Hi can pass through the opening. It will be seen, therefore, thatthe two stop plates H and I! serve to prevent the greater portion of thedirect rays stop plate I6 proback into a cone of light having a focalpoint Y located on the axis passing through the openings 1 and 8 alittle in front of the opening 8.

The stop plate It is so located that its opening 16a which is relativelysmall, usually about inch in practice, coincides exactly with the focalpoint of the lens l5. The light after it passes throughthe focal point Ypasses through the opening 8 and impinges on the light sensitive elementof the light sensitive cell, the parts being so proportioned that thelight will just cover the light sensitive element of the cell.

In explaining the operation of the device, I will first assume that itis desired to position the filament of a lamp 22 in a light unit at thefocal point of the reflector. is snapped into place on the studs 35, 36and 31 and the lamp is illuminated. This causes the light emitted fromthe reflector to follow the path indicated by the broken lines I! and I8in the drawing, thereby concentrating the light rays on the photoelectric cell, and hence causing meter H) to read. The reading of themeter ID will, of course, vary with the intensity of the light, it beingnecessary in order to produce the maximum reading that all of the lightemitted by the reflector should pass through the opening in and strikethe light sensitive cell. Due to the location and arrangement of theparts, before all of the light will pass through the point Y it mustfirst be concentrated at the focal point X, and this will only happenwhen thefllament of the lamp is accurately located at the other focalpoint of the reflector. The position of the lamp may be varied by meansof the adjusting nuts 25, and the operator will adjust these nuts untila maximum meter reading is obtained, whereupon he -observe the meterreading for each lamp, discarding those lamps which produce a lowermeter reading than that of the standard lamp.

Kit is desired to test reflectors, the operator will provide a standardlight unitwith a stand ard lamp which is properly focused in-relation toa standard reflector, and will observe the meter reading. He will thenreplace this standard reflector with those reflectors which are to betested, and will observe the meter readings for each reflector,discarding those reflectors which give a smaller reading than thatprovided by the standard reflector. I

One advantage of a device embodying my invention is that it takes upvery little room.

Another advantage of a device embodying my invention is that it providesa means for deter-' mining when the sockets are accurately located inthereflector assembly, thereby producing a light source for Searchlightsignals which will give the maximum obtainable in beam intensity.

To do this, the light unit- Although I have herein shown and describedonly one means for testing and focusing light signals it is understoodthat various changes and modifications may be made therein within thescope of the appended claim without departing from the spirit and scopeof my invention.

Having thus described my invention what I claim is:

A testing device for use with a light unit comprising a reflector havingconjugate foci and an electric lamp the filament of which is adapted tobe accurately located at one of the foci of said reflector, said devicecomprising a plurality of parallel rods mounted in two spaced endplates, a doublet mounted on said rods between said end plates andhaving a focal point adjacent one end plate and capable of emitting abeam of parallel rays toward the other end plate when a light source isdisposed at said focal point, means on said one end plate for detachablysecuring said light unit thereto in a position in which its axis alignswith the axis of said doublet and its other focus coincides exactly withthe focal point of said doublet, a first stop plate mounted on said rodsbetween the focal point of said doublet and said one end plate andprovided with an opening of such size that the cone of light emittedfrom the reflector will just pass through said opening, a second stopplate mounted on said rods between said doublet and its focal point andprovided with an opening of such size that only enough light to fill thelenses of the doublet is permitted to pass said second plate, acondensing lens mounted on said rods in the beam of light emitted bysaid doublet and arranged to concentrate the light rays at a pointadjacent said other end plate, a third stop plate mounted on said rodsand provided with a relatively small opening which coincides exactlywith the point of light from said condensing lens, a photo electric cellsecured to said other end plate in a position to receive the light raysafter they pass through said third stop plate, and a meter connectedwith said light sensitive element and responsive to the intensity of thelight striking said element, said intensity being a maximum when saidlamp is on focus.

MYRL R. noUGLAss.

